1. Field of the Invention
The present invention relates to a semiconductor light-emitting device, in particular, to a light-emitting device primarily comprised of InP based material.
2. Related Prior Art
FIG. 4 is a cross section showing a structure of a conventional light-emitting device 100, which primarily comprises of InP based material. The device 100, which may be a semiconductor laser diode, includes an n-type InP substrate 101, an optical guiding portion 102 formed on the substrate 101, a current blocking portion 103 provided so as to bury the optical guiding portion 102, and a p-type layer 104 provided on the optical guiding portion 102 and the current blocking portion 103. This p-type layer 104 includes a p-type InP layer in the lower side and a p-type InGaAs layer thereon.
The guiding portion 102 includes, from the side of the n-type InP substrate, an n-type InP layer 105, an active layer 106 on the n-type layer 105, and a p-type layer 106 on the active layer 105. The current blocking portion 103 includes, from the side of the n-type InP substrate, a p-type InP layer 108, an n-type InP layer 109 on the p-type InP layer 108 and another p-type InP layer 110 on the n-type layer 108. Moreover, the device 100 provides two electrodes, one of which is the anode 112 on the p-type InP layer 102 and the other is the cathode 111 on the back surface of the n-type InP substrate.
The device 100 shown in FIG. 4 may be formed by: (1) sequentially growing the n-type InP layer 105, the active layer 106 and the p-type InP 106 on the n-type InP substrate 101; (2) etching these grown layer until the n-type substrate exposes to form the optical guiding portion 102, (3) secondary growing the p-type InP layer 108, the n-type InP layer 109 and the other p-type InP layer 110 on the substrate 101 in selective to bury the optical guiding layer, and (4) third growing the p-type layer 104 and forming two electrodes, 111 and 112. Japanese Patent Application published as JP-H08-250808A has disclosed such device and the process to obtain the semiconductor device with such structure.
The InP substrate, where the device is to be formed thereon, should have high quality as possible, in other words, the substrate should have the dislocations as low as possible. In particular, when the device includes a stress induced multi-quantum well (MQW) structure, the substrate with quite low dislocations is inevitable. Recently, it has been reported that an InP substrate heavily doped with sulfur (S) shows a quite low EPD less than 100 cm−2.
However, the light-emitting device with the structure shown FIG. 4 has an inherent disadvantage when the device is formed on the substrate 101 heavily doped with sulfur (S). That is, the impurities doped in the substrate 101 easily diffuse into the p-type blocking layer 108 during the growth of this p-type layer 108, which disarranges the interface between the p-type layer and the n-type layer to degrade the performance of the device.
The present invention is to provide a structure for the light-emitting device that prevents the inter diffusion of impurities in the substrate to the other layer during the growth of the other layer, even when the substrate is heavily doped to reduce the dislocations.